The logic of this is a bit twisted. I understand the concept of deleting certain tags on upload, but it's ridiculous to hide tags which need removing. It's logical to hide data which is essential, not the other way around.

This tag doesn't "need removing", it just doesn't serve any purpose. Otherwise there would simply be an automatic edit to remove it once and for all. However hiding this tag will prevent people from editing and misreading it.

I agree with the above comments the tag has no practical meaning (which editor you used is a changeset property right now http://wiki.openstreetmap.org/wiki/Changeset#Tags_on_changesets) and you should simply ignore it. There is btw in my opinion at least some useful information left in this tag (and a reason not to just delete all of them at once): a POI tagged created_by is probably worth a survey, it is a long time since it was last touched by someone.

JOSM automatically removes the created_by tag whenever an element with such a tag is edited. So you don't need to delete these tags by hand. Instead, they automatically disappear from the database as part of other edits.

You should not remove the created_by
tag on objects you are not otherwise
modifying. If we wanted to remove them
in bulk we'd do it some other way.

The concept of tags being automatically removed by editors is known as "discardable tags". That page also links JOSM's list of discardable keys. For the most part, it contains superfluous tags from major imports.